In a way, Clay Shirky already addressed this point in Here Comes Everybody: The Power of Organizing Without Organizations when he talked about the difference between a blog of a few followers versus one with thousands: scale impacts the democratization of communication. Digg’s Jake Levine talks about how the bigger social networks are now mutating into more traditional broadcast media. Sorry to say, but I agree. In particular I really don’t like this idea that brands are having “conversations” with the public. A monolog is really not a discussion.
There is an inherent tension in social software between content discovery and the quality of conversation around that content. Group conversations get worse as groups grow, and groups grow as group discovery improves — if it’s easier to find something, more people will find it. Therefore, the easier time I have finding good conversations, the less likely those conversations are to be any good (e.g. Reddit’s front page vs. subreddits).